A vehicle illumination device in which two rotating bodies are mounted on an outer side of a wheel cap (see, e.g., Japanese Unexamined Patent Application Publication No. 2004-90884A), a method of rotating an in-wheel power generator using wind power from outside a wheel cap (see, e.g., Japanese Unexamined Patent Application Publication No. H2-55556A), and the like are known as examples of conventional technology for generating power using the rotational force of a tire.
The techniques disclosed in Japanese Unexamined Patent Application Publication Nos. 2004-90884A and H2-55556A are both techniques that use wind power under atmospheric pressure on the outside of a pneumatic tire. Therefore, the density of the gas that can be used is not in a high state, and thus the wind power cannot be efficiently converted into electric power.